Re: set_bit() is broken on i386?

[Andrew Morton]

Andreas Schwab <schwab@xxxxxxx> wrote:
>
> Trond Myklebust <trond.myklebust@xxxxxxxxxx> writes:
> 
> > On Fri, 2006-01-20 at 19:53 -0500, Chuck Ebbert wrote:
> >
> >> #define ADDR (*(volatile long *) addr)
> >> static inline void set_bit(int nr, volatile unsigned long * addr)
> >> {
> >> 	__asm__ __volatile__( "lock ; "
> >> 		"btsl %1,%0"
> >> 		:"=m" (ADDR)
> >> 		:"Ir" (nr));
> >> }
> >
> > The asm needs a memory clobber in order to avoid reordering with the
> > assignment to b[1]:
> 
> Check out 2.6.16-rc1, this has already been fixed.
> 

No, that doesn't fix this testcase.

We need to somehow tell the compiler "this assembly statement altered
memory and you can't cache memory contents across it".  That's what
"memory" (ie: barrier()) does.  I don't think there's a way of telling gcc
_what_ memory was clobbered - just "all of memory".
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